Sunday, December 16, 2007

Out of Pile excursions by transuranium elements from the Kruemmel reactor?

Om my post of yesterday, I noted that it was unlikely that the transuranium elements reportedly found in Elbmarsch homes came from the Kruemmel reactor. A compilation of ORNL nuclear safety research studies, OUT-OF-PILE STUDIES OF FISSION-PRODUCT RELEASE FROM OVERHEATED REACTOR FUELS AT ORNL, 1955 -1965. G. W. Parker, C.J. Barton, G.E. Creek, W. J. Martin and R. A. Lorenz noted the possible methods of radioisotope transport from a Light Water Reactor into the Environment. These included 1. Fuel Melting, 2. Fuel Oxidation (fire), 3. Gaseous Fission Product Diffusion, 4. Migration of Solid-Phase Fission Products and 5. Compound Formation.

Of these options 1 and 2 seem clearly out since both would assume a major reactor incident. ether a reactor meltdown or a reactor fire. 3. Might be possible, but would not explain the presence of PU238,239,240, AM241 and CM244 in Elbmarsch homes. The Parker el al study reports, "In heterogeneous fuel systems, solubility of the fission products in the fuel matrix and cladding is of little significance as a mechanism affecting release except perhaps at temperatures approaching the fuel melting point. Even partially melted fuel plates of aluminum alloy from a fuel melting accident in the Oak Ridge Research ReactorZ3 showed no significant migration of fuel or cladding penetration in a part of the fuel plate very close to the melted region, presumably because such a process is strongly time dependent."

Finally we have compound formation. Parker et al comment:Compound formation between fission products and fuel components is normally not significant; however, in theory it should occur to some extent between volatile elements such as cesium and the halogens when fuel rods are operated at temperatures high enough to permit distillation of these fission products and condensation in the cooler parts of the can. Such compounds, however, have relatively low stability and they would probably dissociate in the event of high-temperature cladding rupture, Experiments on fission-product release from uranium-aluminum alloy failed to show appreciable compound formation when cesium and iodine were released simultaneously by melting, even though the aerosol of iodine and cesium was allowed to age for an extended period in the same concontainer.

This was demonstrated by the diffusion tube method. Compound formation may be of somewhat more significance in the case of pyrocarbon-based fuels. The rapid diffusion of soluble but relatively unstable carbides of strontium and barium may account for the observed high rates of diffusion of these elements. The behavior of cesium, which also diffuses rapidly in graphite-matrix fuels, is affected by the formation of interlamellar compounds, such as CsC,. Other fission products (e.g., zirconium-niobium) are immobilized as carbides because of the high temperature stability of the compounds. It seems likely, however, that compounds which form when two fission-product elements are deposited on the same surface may be of more importance than those formed in the fuel.

It has been reported that there is evidence of formation of a uranium iodide compound when irradiated uranium is melted in pure helium. Since fission-produced iodine atoms are surrounded by uranium atoms, it appears that favorable conditions for reaction exist.

Uranium iodides are easily oxidized and it is highly unlikely that fuel materials will be surrounde'd by pure, non-oxidizing gases in a reactor accident, hence it seems probable that uranium iodide formation would not significantly affect release of fission-product iodine from uranium or uranium alloys under accident conditions."

Well the short of it is that something very nasty and destructive has to happen inside a reactor for transuranium elements to have escaped.

Since "spent" reactor fuel is stored underwater, it is even less likely that spent fuel would escape from holding ponds. We might expect contamination in the ground water or in the Elba River from spent fuel, but not in household dust. We are thus left with the word Chernobyl if we seek a reactor source of the transuranium elements found in Elbmarsch homes. Chernobyl would certainly not explain the Elbmarsch leukemia cluster.